This invention relates to melting and refining glass for the manufacture of glass articles, particularly for the manufacture of flat glass. More particularly, this invention relates to the application of heat to glass batch materials in a glassmaking furnace adapted for heating such materials as they float on and advance along the surface of a pool of molten glass maintained in the furnace.
Glass batch materials have been melted and molten glass refined and conditioned by the application of heat to glass batch and to molten glass from a variety of sources in furnaces of varied design. Today, for the commercial production of glass products on an efficient scale, molten glass is prepared for forming in furnaces of several general kinds. These are fossil-fueled furnaces, such as regenerative furnaces and recuperative furnaces, electric furnaces of the kind illustrated in U.S. Pat. No. 2,225,616 and U.S. Pat. No. 2,225,617. There are fossil fuel-fired furnaces which include electric-boosting electrodes as shown in U.S. Pat. Nos. 2,397,852, 2,600,490, 2,636,914 and 2,780,891. These patents and many other patents and publications illustrate that for many years there has been widespread interest and activity in the use of electricity to melt glass batch and to heat molten glass.
According to the prior art, heating electrodes have been employed in glassmaking furnaces in several different ways. For example, electrodes have been used in batch charging kilns, as in U.S. Pat. No. 2,397,852, and along the walls of furnaces, as in U.S. Pat. No. 2,975,224, to heat naturally cold regions of the furnaces where heat is normally lost to the outside environment. When used near side walls of a horizontal furnace, electrodes have served to establish convective flows in molten glass which keep unmelted batch in the center of the furnace away from its side walls.
In general, when both electricity and fossil fuels have been used to provide heat to the same glassmaking furnace, the fossil fuels have been employed to melt glass batch in the region of the furnace where batch is advancing freely through the furnace from its charging kilns. Electrodes have been positioned in the furnace well downstream from where batch is charged in order to heat molten glass beyond the region of unmelted batch and to strengthen the convective flow, known as the "spring zone" flow, within the molten glass as shown in U.S. Pat. Nos. 2,512,761, 2,636,914 and Canadian Pat. No. 634,629.
Given a comprehensive view of the prior art relating to the use of electric heating electrodes in glassmaking furnaces, it is apparent that it is well known that such devices may be used to advantage. The questions facing an artisan in the glassmaking art are not concerned with whether or not to consider the use of heating electrodes. Rather, the questions are: Where should heating electrodes be placed in a furnace? How should those electrodes be used in combination with the other elements of the furnace to achieve a desired benefit?
The specific problems confronting the present applicants have not been considered in the past as being directly relevant to electric melting and heating glass. In a horizontal glassmaking furnace, whether regenerative or recuperative, there are undesired fuel inefficiencies and there is a problem of unmelted batch being blown from the furnace through checker brick packing to the stack or exhaust system serving the furnace. The first of these problems would invite at least a study of the potential of electric heating, but the applicants have discovered that both problems can be greatly alleviated by a particular application of electric heating to a glassmaking furnace.